Some physicians and cholesterol technicians use the ratio of total cholesterol to HDL cholesterol in place of the total blood cholesterol. The ratio is obtained by dividing the HDL cholesterol level into the total cholesterol. For example, if a person has a total cholesterol of 200 mg/dL and an HDL cholesterol level of 50 mg/dL, the ratio would be 4:1. The goal is to keep the ratio below 5:1; the optimum ratio is 3.5:1.
Source: http://www.americanheart.org/presenter.jhtml?identifier=1516